Most of the nearly 14 million cancer survivors living in the United States (US) today received chemotherapy, a mainstay cancer treatment. Many chemotherapy drugs are neurotoxic, and almost all who receive these drugs will develop chemotherapy-induced peripheral neuropathy (CIPN). Common CIPN symptoms include numbness, tingling, and neuropathic pain in the extremities. CIPN can necessitate chemotherapy dose reductions, potentially compromising cancer treatment efficacy. Symptoms can become chronic, and functional disability and diminished quality of life are common adverse outcomes. Despite these debilitating consequences, researchers have been unable to find effective CIPN treatments in part due to CIPN measurement limitations. More specifically, there is no consensus regarding which CIPN measurement approach to use in intervention studies. Toxicity grading scales such as the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) are the most commonly used outcome measures utilized in today's CIPN intervention research. However, grading scales have been repeatedly shown to be insensitive and unreliable. The lack of a gold-standard measure limits our ability to build upon the knowledge gained from one study to the next, and insensitive measures may not detect improvements in CIPN resulting from a truly effective experimental treatment. Thus, this research will address these two problems; 1) there is no gold-standard CIPN measurement approach, and 2) psychometrically weak measures are commonly used to measure CIPN treatment efficacy. It is important to address these CIPN measurement problems because they pose a barrier to discovering new treatments for a prevalent and distressing problem. The long-term goal of this research is to identify a superior CIPN outcome measure that will aid in the future discovery of effective CIPN treatments. To accomplish this goal, we will conduct a secondary data analysis followed by a mixed methods, prospective, longitudinal study to extensively examine the psychometric properties of a promising CIPN patient-reported outcome measure (PRO), the European Organization of Research and Treatment of Cancer Quality of Life Questionnaire-Chemotherapy-Induced Peripheral Neuropathy Scale (QLQ-CIPN-20). The study Specific Aim is to evaluate QLQ-CIPN-20 reliability, validity, sensitivity, and responsiveness to change. The study results will be highly generalizable and will make a substantial contribution to symptom management science because the end product will be a refined and fully tested CIPN PRO measure. This measure will be ready for use in future small- and large-scale studies designed to uncover effective interventions to improve clinical outcomes and quality of life for individuals who receive neurotoxic chemotherapy.